Re: [PATCH RESEND v2 1/2] serial: earlycon: add uart_clk_freq parameter

[Geert Uytterhoeven]

Hi Markus,

On Tue, 9 Jun 2026 at 00:40, Markus Probst <markus.probst@xxxxxxxxx> wrote:
> Add `uart_clk_freq` parameter to `setup_earlycon`. This allows the
> options string to be reused with `add_preferred_console`, while still
> allowing to set the uart clock frequency. This will be used in the
> following commit ("ACPI: SPCR: Support UART clock frequency field").
>
> No logical change intended.
>
> Signed-off-by: Markus Probst <markus.probst@xxxxxxxxx>

> --- a/drivers/tty/serial/earlycon.c
> +++ b/drivers/tty/serial/earlycon.c
> @@ -135,11 +135,14 @@ static int __init parse_options(struct earlycon_device *device, char *options)
>         return 0;
>  }
>
> -static int __init register_earlycon(char *buf, const struct earlycon_id *match)
> +static int __init register_earlycon(char *buf, unsigned int uart_clk_freq,
> +                                   const struct earlycon_id *match)
>  {
>         int err;
>         struct uart_port *port = &early_console_dev.port;
>
> +       port->uartclk = uart_clk_freq;

Who is actually consuming this value?
Earlycon typically works with the serial console, as configured before
Linux boot by the firmware.
The Microsoft doc referenced in patch 2 seem to agree with that:

   "On a system where the BIOS or system firmware uses the serial
    port for console input/output, this table should be used to convey
    information about the settings, to ensure a seamless transition
    between the firmware console output and Windows EMS output."

> +
>         /* On parsing error, pass the options buf to the setup function */
>         if (buf && !parse_options(&early_console_dev, buf))
>                 buf = NULL;

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds